The invention is directed generally to broad band switching systems. More specifically, the invention is directed to leaky bucket methods for packet switching systems wherein the binary character rate for every virtual connection is monitored and limited in a message cell stream that is transmitted according to an asynchronous transfer mode or method (ATM) and that carries message cells of a plurality of virtual connections having a defined plurality of binary characters.
It is known in broad band switching systems, wherein information packeted in message cells is asynchronously transmitted over virtual connections to declare a maximum binary character rate, among other things, when setting up a respective, virtual connection between the appertaining subscriber location and the broad band switching system. In order to avoid overload phenomena, the binary character rate for every virtual connection must be monitored and, potentially, limited at the access locations of the broad band switching system or at the exchange terminating equipment of the switching nodes of the broad band switching system. Equipment for monitoring and limiting binary character rates are generally referred to as policing equipment.
It also is known (e.g., from "New Directions in Communications" A . . . 1-A . . . 8 by J. B. Turner, in "International Zurich Seminar on Digital Communication", March 1986, fully incorporated herein by reference) to allocate a forward-backward (up/down) counter in a switching node of a broad band switching system to every subscriber location connected to this switching node, this forward-backward counter counting the message cells transmitted by the respective subscriber location and lowering the momentary counter reading at defined points in time in accordance with the binary character rate declared by the respective subscriber location. When the momentary counter reading exceeds a value prescribed by the respective subscriber location, then the switching node recognizes an overload. This is known as the "leaky bucket method".
In such a leaky bucket method, it is not necessary to recalculate for every virtual connection the counter readings of all established virtual connections during every message cell cycle wherein a message cell can arrive at the same time as the arrival time of the most recent message cell belonging to the connection is stored; and the counter reading of the connection to which a message cell belongs is only recalculated given the arrival of this message cell. The current counter reading z.sub.na for a virtual connection n is thereby calculated according to the expression ##EQU1## whereby z.sub.na-1 is the counter reading for the virtual connection n before the arrival of the message cell now under consideration
d is the current point in time PA1 t.sub.ln is the point in time of the arrival of the immediately preceding message cell belonging to the same virtual connection PA1 t.sub.dn is the shortest allowable chronological spacing of two successive message cells belonging to the virtual connection under consideration. PA1 asynchronously transmitting message cells belonging to a plurality of virtual connections, every message cell comprising a known plurality of binary characters; PA1 establishing a binary character rate B.sub.req for every virtual connection; maintaining a counter reading for every virtual connection; calculating a current counter reading according to the expression ##EQU2## upon arrival of a message cell for the virtual connection n to which this message cell belongs, whereby PA1 discarding the message cell under consideration when a defined counter reading is exceeded by the current counter reading; and PA1 otherwise forwarding the message cell now under consideration, whereby two memory locations are provided for storing the shortest allowable timing between two message cells belonging to the same virtual connection, a multiple of the shortest allowable timing being stored in one of said two memory locations and a quotient of this multiple and the shortest allowable timing itself being stored in the other of said memory locations, and whereby a quotient of the contents of both memory locations is formed in the calculation of the current counter reading for the generation of the shortest allowable timing.
When a broad range of, for example, five orders of magnitude, of binary character rates is monitored in this way, then the numerical values to be processed exhibit a correspondingly great value range, this requiring a correspondingly great capacity of the memory in which the values are stored. Over and above this, a processing of numerical values having a great value range and the necessity of implementing floating decimal point operations is opposed by a reduction of the time requirement for the processing.